Telephone system



Oct. 18, 1932 T. F. cRocKl-:R ET AL 1,883,589

TELEPHONE SYSTEM Filed Dec. 18, 1930 13 Sheets-Sheet 1 Q m. mv n m m. v m. N

'Oct. 18, 1932. r. F. cRocKER ET AL TELEPHONE SYSTEM Filed Deo. 18. 1930 13 Sheets-Sheet 2 Inuen nrs Thomas F.' [f1-baker UH: DI- E TPIEFFI Och 18, 1932. A TQ F. cRocKl-:R ET AL 1,883,589

TELEPHONE SYSTEM Filed De. 18. 195o 1s sheets-sheet s T0 SEL. BANKS ToLL/A/E Inval-11 nrs Thomas Ff [In: cker oct. 1s, 1932.

@un www www C my 1932 T. F. cRocKER ET AL L883589 TELEPHONE SYSTEM Filed Dec. 18, 1950 1,3 Sheets-Sheet 5 T. F. CROCKER ET AL TELEPHONE SYSTEM' Filed Dec. 18, 1930 13 Sheets-Sheet 6 Thomas F. Erzieher' UEE? E. Thal-P @Ct 318,'3932 T. F. cRocKER ET Aa. 1,883,589

TELEPHONE SYSTEM Filed Dec. 18. 1930 13 Sheets-Sheet 7 T. F. CROCKER ET AL @cm my E932.

TELEPHONE SYSTEM Filed Dec. 18. 1950 13 Sheets-Sheet 8 @QL 31% E932, T. F. @RQCKER ET AL gs@ TELEPHONE SYSTEM Filed Dec. 18, 1930 13 Sheets-Sheet 9 TUA/E HEY FLASH InLrEI-LCJFE Thames F1. Cracker @ein g i932., T. F. CROQKER ET AL,

TELEPHONE SYSTEM Filed Dec. l8I

1930 13 Sheets-Sheet 10 Inuen nrs' Thomas F. Erm'ckar Uu: Dr E. Tharp @ai l, @32 T. F. CROCKER ET AL 3938395@ TELEPHONE SYSTEM Filedpec. 18, leso 1s sheets-sheet 11 'I1-mentors 'Tl-Lamas F.' Cracker UTE'EF E. Tharp LSSBS@ @ma E87 @El T. F. CROQKER ET AL.

TELEPHONE SYSTEM Filed Deo. 18, 1930 l5 Sheets-Sheet l2 @et i8? w32. T. F. CROCKER ET AL TELEPHONE SYSTEM Filed Deo. 18. 1930 13 Sheets-Sheet l5 ESQ..

S :.w M@ s w @E .w ww JM@ mw 2m vw NGE ENS Inusn mrs 'Tl-immens F Cracker Uu: nr E. Thal-F Patented Oct. 18, 1932 UNITED sTATEs PATENT OFFICE THOMAS F. CROCKER, OF CHICAGO, AND VICTOR S. THARP, OF ELMHURST, ILLINOIS, ASSIGNORS. BY MESNE ASSIGNMENTS, TAO ASSOCIATED ELECTRIC LABORATORIES, INC., OF CHICAGO, ILLINOIS, A CORPORATION OF DELAWARE TELEPHONE SYSTEM Application ified December 18, 1930.` Serial No. 503,164.

is the simplification of switchboards, switch-I ing apparatus and operating methods for enabling the toll operators to establish and supervise connections more eiiiciently than is possible with present equipment.

In present day practice, all toll switching for an exchange area is centralized at a. toll switchboard. The switchboard ordinarily consists of inward, recording, and delay positions. The number of positions of each class will, of course, depend on the volume of trailic to be handled. Incoming calls from other exchange areas are answered'by switching operators at the inward position and are either completed directly or transferred to a delay position for completion. Through calls, that is, calls in which the switchboard serves as a tandem switching point, are handled at the inward positions in much the same manner as incoming calls. In the case of outgoing toll calls, the calling subscriber will ordinarily call a special number to obtain a connection to a recording position.- The recording operator will make out a ticket for the call and may either complete the call directly or pass the ticket to a delay position from which the call will be completed later. f'

The toll switchboard which comprises a part of the present invention includes the more or less standard position arrangement above described. Key controlled link circuits have been provided instead of the usual cord circuits for interconnecting lines and'trunks. New and improved switching apparatus has also been provided for facilitating the establishment of connections.

One of the features of the invention is the arrangement for preventing the connection of a toll line with a trunk until the connection over the trunk line has been completed. This arrangement prevents the false operation of signals by the return of battery and ground from the switching apparatus employed in 60 setting up a connection. Another feature is the arrangement whereby an incoming call may be transferred to another position prior to answering bythe operation of the release key of the link seized by the calling line. Another feature is the automatic ringing arrangement whereby on calls from certain positions ringing current is automatically applied to the called toll line or subscribers line. Manually controlled reringing is also provided at these positions. A still further feature is the arrangement for indicating the group to which a calling line belongs. This is particularly advantageous in a system employing automatic call distribution as is the case in the present system. Another feature is the provision of a toll transmission selector which disconnects battery and ground from the trunk or the establishment of a connection with a subscribers line whether idle or busy, or on finding all trunks in the called level busy. An incidental feature is the arrangement for connecting the impulse relay of the transmission selector to the supervisory conductor to give line seizure supervision. This circuit also serves to maintain the impulse relay operated until it is disconnected therefrom on the call being answered. This disconnecting of the impulse relay provides answering supervision. A still further feature is the ring-back switch for enabling a toll recording operator to recall a party line subscriber without releasing the original connection.

The foregoing features, together with others not specifically mentioned, will be discussed further in connection with the description of the operation of the invention, reference being had to the accompanying drawings comprising Figs. 1 to 13, inclusive. The drawings show, by means of the usual circuit diagrams, the essential equipment of a complete toll service switching system. Fig. 1 shows an operators impulse sending device including a key set, control relays, and register-sender as provided for each position of the switchboard. Fig. 2 shows the telephone set and position apparatus as provided for each inward position. Fig. 3 shows a link circuit associated with the position apparatus of Fig. 2. In this figure there is also shown an incoming toll line and its associated line-switch. F ig. 3A shows a link circuit associated with another inward position and a toll line with its associated lineswitch. Fig. 4 shows a. toll selector associated with the link circuit of Fig. 3. Fig. 5 shows the telephone set and position apparatus as provided for each delay position. Fig. 6 shows a link circuit associated with the position apparatus of Fig. 5. ig. 7 shows a toll transmission selector accessible to the various toll selectors. Fig. 8 shows a combination local and toll party line connector switch. Fig. 10 shows the telephone set and position apparatus as provided for each recording position. Fig. 11 shows a recording-completing link associated the position apparatus of Fig. 10, a subscribers line and lineswitch, and a local selector. Fig. 12 shows a ring-back switch aociated with the position apparatus ofF ig. 1G. Fig. 13 is a layout diagram showing how the various sheets of drawings should be arranged to be best understood.

Referring now to Fig. 1, key set KS is the usual type of key set comprising ten digit keys, a Start key and an Error7 key. Each time az key is operated the corresponding digit is set up in the register. An operator can thus record the number of a wanted line by operating the keys in accordance with the of the number. The register and associated sender shown in skeleton form, may be of any suitable type adapted to register and n'ansmit numbers of ive or more digits. A register-sender of the type disclosed in Patent No. 1,800,321, granted April 14, 193i, to N. H. Saunders et al., modified for the transmission of loop impulses is particularly suitable. Suliicient apparatus has been shown to indicate the modifications required in the sender disclosed i'n the above referred to application to adapt the same to transmitloop impulses. The modification consists principally of the addition of a second impulsing conductor which is connected to springs of the interrupter, start relayr and stop relay in place of the ground connection shown in the application. A further rnodiiication consists of the use of the holding conductor for initiating the operation of the interrupter which is entirely satisfactory in this case. It will be noted that the designations applied to the relays and conduors of the register sender are the same as those used in the above application.

Reference to Fig. 13 will indicate that Fig. 1 is designed to cooperate with Figs. 2, 5, and 10. The various conductors connecting these figures have been designated accordingly.

In Fig. 2 is shown an operators telephone set 0T, position apparatus PA, and dial D. Each inward position is equipped in this manner. The position apparatus ispermanently associated with a number of link circuits which are operatively connected thereto one at a time by the operation of the answering keys of the link circuits. When a link circuit is connected to the position apparatus, the talking conductors of the link are looped through the apparatus with the telephone set connected in bridge. Ringing and splitting keys K1 and K2 such as are commonly used in toll cord circuits are provided. 'These keys are of the double throw type arranged to lock only when operated to splitting position. Release key K is a non-locking key for permitting the release of partially established connections without releasing the associated link. The position apparatus is normally associated with the register-sender apparatus of Fig. 1 through contacts of key K20. The dial D which is provided for use in case the register-sender fails to function properly may be connected up by operating key X20. The register-sender is operatively connected to the position apparatus on the operation of the Start key while the dial is connected responsive to its irst movement from normal position. The operative connection of the calling device is maintained automatically until a connection is completed wherein the calling device is released. Dial pilot lamp L glows when the calling device is connected up in the above manner. The position apparatus is also arranged so that a ringing impulse is automatically sent out in all calls completed from the inward position. The ringing keys above referred to are therefore required only for re-ringing and for certain supervisory operations.

ln Fig. 3 is shown a link circuit L associated with the position apparatus of Fig. 2. The link circuit is provided with a talking and monitoring key K3, a release key K4, a, line lamp L2, a busy lamp L3 and a supervisory lamp L4. A selector (Fig. 4) is permanently and individually associated with the link. Link circuits such as L are accessible to lineswitches LS which terminate incoming toll lines. The trunks outgoing from the banks of the lineswitches will be distributed over the various inward positions, for example, the trunk from the fifth set of contacts extending to link L of one position,

and the trunk from the sixth set of contacts extending to link L3 (Fig. 3A) of another position. It will be noted that in the bank level engaged by wiper 338, the odd numbered contacts are multipled and connected to lamp L1 while the even numbered contacts are multipled and connected to a corresponding lamp at a different position. Corresponding contacts of this bank level will be multi led for the lineswitches of all toll lines o one group, that is, toll lines from the same exchange area. Each group of toll lines will be arranged in this manner and an identification lamp corresponding thereto will appear in each position. Lamp L19, incidentally, is a group lamp for the group oE toll lines includin the line shown in Fi A. It will be note that the double ringing relay 301 is permanently bridged across the trunk in series with battery and ground. It ma be noted, however that the lower or attery connected winding is of extremely high resistance and is ineffective' as far as operating the relay is concerned. The arrangement is provided for the purpose of keeping the negative line conductor alive which reduces faults due to dust accumulating on the relay contacts.

Fig. 3A shows alineswitch LS2 and a link circuit L3 which are similar to corresponding apparatus shown in Fig. 3. The toll line terminating in lineswitch LS3 is assumed to be in a different group from the toll line shown in Fig. 3. The link circuit will connect with position apparatus such as that of Fig. 2 land will have its associated selector similar to selector S (Fig. 4).

In Fig. 4 is shown a toll selector S associated with the link circuit L of Fig. 3. This selector' is of the well known Strowger vertical and rotary type provided with a fourth wiper for extending a supervisory circuit. The selector has 'access to toll lines, to transfer circuits at the delay positions, and to a toll switch train. For convenience of description, toll lines of the group including the toll line of Fig. 3A have been shown terminating in the fourth level of the selector banks. Toll service trunks have been shown terminating in the third level of the banks and transfer trunks terminating in the second level of the banks.

In Fig. 5 is shown an operators telephone set OTl, position apparatus PAl and dial D1 as provided for each delay position. This apparatus is similar to that of the inward position shown in Fig. 2 except that a calling device transfer key K7 and a coin control key K8 have been provided. The transfer key is necessitated by the double ended llnk circuits associated with this position. The control key is provided for controlling the collection and refund of coins in calls involving pay-station lines as 'it is assumed that calls of this class will be handled by a delay operator rather than by an inward operator. A further modification is the elimination of the automatic ringing feature which is considcred undesirable at the delay position. Aside from points above noted, the equipment shown in this figure correspondsexactly with that shown in Fig. 3. The registersender apparatus for this position will be the same as that shown in Fig. 1 and conductors extending thereto have been designated accordingly and so placed that they line up with corresponding conductors of Fig. 1 vhen that figure is placed to the left of Fig. 6 shows a double ended link circuit L1 and its associated selectors S1 and S2.

This link circuit is one of a numberassociated with each delay position (Fig. 5) and is used to set up tail-to-tail connections. The link circuit is provided with the usual talkin and monitoring key K10, release key K11, recall lamp L9, su ervisory lamp L10 and busy lamp L11. electors S1 and S2 are similar in all respects to selector S (Fig. 4) and have therefore been shown only in skeleton form. The banks of these selectors are multipled with the banks of selector S on all levels except the second which is left vacant. f

The toll transmission selector TTS shown in Fig. 7 is of the well known Strowger vertical and rotary type arranged to rovide the transmission efficiency required 1n toll service. This selector is accessible to the toll selectors associated with the inward and delay positions and in turn has access to intermediate selectors or toll connectors, depending upon the size of the system. The selector is arranged to give both tone and flash busy supervision. Line seizure, answering,

and disconnect supervision are given over a f fourth conductor. v

Fig. 8 shows a combination local and toll party-line connector which is -accessible to toll transmission selectors such as selector TTS and to local selectors (not shown). The connector is arranged to feed battery to the calling and called subscribers' and to ring automatically when used in local connections. When used in toll connections, the talking conductors are extended through to the called line without bridges or condensers and ringing is under control of the operator. The connector has access to party lines of which the line extending to substations T and T1V is shown. It will be understood, of course, that the system will include the usual individual line and rotary connectors in addition to the party line connector shown.

Fig. 9 shows a transfer link circuit over which calls transferred from the inward and recording positions are completed. This link circuit is associated with the position apparatus of Fig. 5. The link circuit is provided with the usual talking and monitoring key K12, release key K13, line lamp L12, supervisory lamp L13 and busy lamp L14. Selector S3 which is individual to the link L2 is identical with selector S (Fig. 4) and its banks are multipled with the banks of selector S on all levels except the second.

In Fig. 10 is shown an operators telephone set 0T2, position apparatus PA2, and dial D2 for a recording position. This equipment is the same as that provided for the inward positions (Fig. 2) except that Vthe automatic ringing feature has been eliminated and a calling device transfer key K16 has been provided. The conductors extending to the right-hand edge of the sheet join with similarly designated conductors in Fig. 1. f

In Fig. 11 there is shown a link circuit L4 which is accessible to subscribers over a first selector and toll-recording trunk. r[he liul: circuit is associated with the recording position apparatus of Fig. 10 and is )rovided with the usual talking and monitoring key 1(18, release key KIS, supervisory lamp L16, busy lamp L17 and line lamp L18. Selector S4 associated with this link circuit is the same as selector S (Fig. 4), and its banks are multipled with those of selector S on all levels except the third in which the toll service trunks are accessible. Substations T2 and T3 and the associated party line terminating in lineswitch LS1 are also shown in this figure. Selector S5 is au ordinary Strowger type selector accessible to lineswitches such as LS1 and having access to local trunks (not shown) and to toll recording trunks such as the trunk terminating in link L4.

The ring-back switch shown in Fig. 12 is associated with the recording position appas ratus shown in Fig. 10 and has access by way of its banks to the toll recording trunks including the trunk shown in Fig. 11. The various trunks are identified by two digit code numbers. The switch is provided with an auxiliary ringing current selecting switch for selecting ringing current of the frequency required to signal a particular substation on a party line.

Having briefly described the apparatus comprising the invention, a detailed description of the operations involved in setting up various calls in a system employing the invention will now be given.

and answered in the same manner'and will be considered together. It will be assumed,

. by way of example, that an operator at a distant toll board has extended a connection over the toll linev comprlsing conductors l391--392 which terminates in lineswitch LS.

Ringing current applied to the toll line at the distant toll board energizes relay 302 which is bridged across the trunk conductors in series with condenser 350. Relay 302 is equipped withl a mechanically locking armature which locks in operated position when the relay is energized and remains in this position until unlocked by relay 303. Relay 302 on operating completes a circuit for relay 305 by Way of contacts 313 and 345. Relay 305 operates, completes a circuit at contacts 329 forvswitching relay 304 and stepping magnet 306 in series, and at contacts 328, connects test wiper 335 between the relay and the magnet. The contact engaged by wiper 335 in normal or home position is permanently connected to ground. This ground shunts relay 304 and energizes magnet 306 which interrupts its own circuit at contacts 333. On releasing, magnet 306 advances the wipers one step and closes contacts 333. If the trunk terminating in this set of contacts is busy, the stepping operation is repeated. The wipers are thus moved ahead, step by step, until an idle trunk is found, whereon relay 304 is no longer slumted and operates to open the stepping circuit. It may be assumed that the trunk selected isl the one comprising conductors 340-344 terminating in link L. Relay 304 on operating completes various circuits including the extension of the toll line conductors through to wipers 334 and 339 at contacts 316 and 326 respectively. The circuit of relay 305 is opened at contacts 345 and ground through contacts 313 is extended via contacts 320, resistance 387, wiper 337, conductor 342, contacts 362 and relay 353 to bat tery. Relay 303 is connected in parallel with relay 353 at contacts 346, but due to the value of resistance 387, relay 303 does not energize at this time. Relay 353 energizes over the above circuit and completes a circuit from ground through normally closed contacts of rey K4 and contacts 368 for the lower winding of relay 354. Relay 353 also completes a. circuit for lamp L2 at contacts 369 and the lamp glows to indicate an incoming vcall on link L. Relay 354 energizes, applies ground to conductor 341 at contacts 370 to hold relay 304 of the lineswitch operated, completes a locking circuit for its own lower winding at contacts 372 and completes a circuit for busy lamp L3 at contacts 373. Lamp L3 will remain lighted throughout the connection. The toll line will be marked busy in the banks of the toll selectors by ground via either contacts 330 or 347.

Transfer of incoming call The operator may now answer the call, or if too busy, may transfer it to a different inward position for answering. The transfer is effected by momentarily operating key K4 to open the circuit of relay 354. Relay 354 on releasing opens the holding circuit of relay 304 which also releases. Relay 304 completes circuits for relay 305 and magnet 306 simultaneously, the latter circuit including wiper 336 and contacts 327 and 317. The magnet will operate as will relay 305 and the wipers will be advanced a step whereon the trunk engaged will be tested as previously described. The iirst idle trunk found will be seized. The call will thus be extended to a ditl'erent position according to the bank multipling arrangement in use. The call will operate the signal relays of the last seized link n elgxctly the same manner as described for Answering incoming call To answer an incoming call on link L the operator will operate'key K3 to the left. A circuit is thereby established for the upper winding of relay 351 by way of contacts 389 conductor 215, and contacts 234. Relay 351 operates and completes a holding circuit for its lower'winding by way of contacts 360, winding of relay 352, contacts 392, conductor. 212, winding of relay 203, to ground. Relay 203 and relay 352 operate in-series with the lower winding of relay 351 and effect various circuit changes which will be considered later. Relay 351 on operating opens the direct connection between the incoming and outgoing conductors of the link circuit, and loops them through the position equipment, the

circuits being, respectively, conductor 340, contacts 357, conductor 223, contacts 235 and 237, conductor 222, contacts 359 to the upper talking conductor of the link circuit, and conductor 344, contacts 365, conductor 220, contacts 236 and 240, conductor 221, and contacts 364 to the lower talking conductor of the link circuit. Relay 351 also disconnects relay 353 from conductor 342 aty contacts 362, and at contacts 361, connects direct ground to this conductor to energize relay 303 of the toll line. Relay 303 on operating unlocks relay 302 and opens the bridge across'the trunk line at contacts 314. A circuit is closed for group lamp L1 at contacts 315, and the lamp glows to indicate the particular group of trunks from which the call originated. Relay 353 restores after its circuit is opened, opens the original energizing circuit of relay 354 atl contacts 368, and opens the circuit of line lamp L2 at contacts 369. Relay 354 remains energized over its previously-traced' locking circuit. Lamp L2 is extinguished at this time, but lamp L3 continues to glow to mark the trunk busy. As previously mentioned, relay 352 operates in series with relays 351 and 203. This relay prepares a holding circuit at contacts 367 for maintaining the relays energized in case key K3 is restored to normal before the calling operation has been completed. This latter circuit will be better appreciatedfwhen the operation of the register sender is considered later on. Relay 203 upon operating, as above mentioned, connects the operators set across the talking conductors looped through the position equipment by way of contacts 230 and 231. The original energizing circuit of relay 351 is A opened at contacts 234 and ground is applied to conductor 28 at contacts 228 to prepare the register to receive and record digits and to start the sender interrupter. The inward operator may now converse with the calling operator and obtain the necessary information regarding the connection desired.

Extension of through call It will be assumed that the call is a through ductors 391-392 shownin Fig. 3A, accessible in the fourth level of the toll selector banks. It will also be assumed that the register-sender (Fig. 1) is to be used in establishing the. connection. The inward operator on receiving the necessary information actuates digit key 4 of the key set KS (Fig. 1) and the digit 4 will be recorded on the register. The operator will then actuate start key ST, thereby closing a circuit including contacts 20 for relay 11. Relay 11 on operating prepares a circuit for itself in series with relay 12 of contacts 17, and at contacts 15 and 16, respectively, connects ground to conductors 29 and 30, The operation of theregister is such that as soon as the first digit is recorded, ground is connected to conductor 322, thereb energizing relay 13 of the relay group CR. elay 13 prepares the sender-start circuit by closing contacts 22 and prepares a circuit for relay l2 at contacts 23. When the operator releases the start key, the original energizing circuit of relay 11 is opened and the short-circuit is removed from relayv 12, thereby permitting this relay to energize in series with relay 11. Relay 12 on operating, closes the sender-start circuit at contacts 18, prepares a holding circuit at contacts 19, opens the original energizing circuit of relay 11 at contacts 20, and completes a circuit for relay 14 at contacts 21. Relay 14 energizes and transfers the holdin circuit from conductor 28 to contacts 19 y way of contacts 25, thereby rendering the register-sender independent of ground from the operators position equipment. Referring now to the position equipment, relay 208 energizes from ground via conductor 29 and contacts 266, short -circuits relay 207 by closing contacts 253, connects an additional ground to conductor 30 at contacts 254, and at contacts 255 completes a circuit for relay 209. Relay 209 operates, closes a circuit for the dial pilot lamp L at contacts 242, prepares the automatic ringing circuit at contacts 256, and completes the preViously-referred-to holding circuit for relays 203, 352, and 351 at contacts 257. Relays 205 and 206 operate initially from round via conductor 30 and contacts 268. elay 205 on operating opens the previously-traced loop through the position and extends the outgoing end by way of contacts 23S-239, contacts 248 and 250, contacts 253, contacts 262 and 264, conductors 213 and 213, to the impulsing contacts of the sender. In the sender a loop circuit is completed through normally closed contacts of relay 502 so that at this time no impulses are transmitted even though interrupter I is operating continuously. Relay 206 in addition to closing points in the above control circuit, connects ground from the normally-closed contacts 258 of key K3, over contacts 249, conductor 216, contacts 388 and 366, upper Winding of relay 354, lower winding of relay 355 to battery. Re-

lower windings of relay 402, to battery and ground, respectively. Relay 402 energizes and completes a circuit at contacts 419 for re-` lay 403. Relay 403 energizes, prepares the impulsing circuit at contacts 422, and opens a point in the release circuit of contacts 423. The selector is now ready to receive impulses. A short time after the operation of the -Start key, that is, after an interval Sullicient to permit the various relays to operate as described, relay 502 of the sender is energized to remove the short circuit from the impulsing contacts of the sender interrupter I. The sender now transmits impulses 'over the loop until four impulses have been transmitted whereon the sender, under control of the register upon which this digit has been set up, causes relay 503 to operate and again short circuit the impulsing contacts. Relay 502 restores and closes the original short circuit of the impulsing contacts and relay 503 restores in preparation for terminating the next series of impulses. It will be seen, thus that the impulses are transmitted in a Well-known manner according to the setting of the register, and that these impulses serve to operate the switch associated With the link circuit. Referring now to selector S, relay 402 responds to the impulses in the usual way and transmits four impulses by way of contacts 420 and 422 to relay 404 and vertical magnet 406 in series. Relay 404 operates responsive to the first impulse, and, due to its slow-releasing characteristics, remains operated throughout the series of impulses. The stepping magnet responds to each impulse and raises the wipers step by step to the called level. Off-normal contacts 424 and 427 close on the first vertical step of the Wipers, the latter contacts completing a circuit for relay 405 which operates and locks by way of interrupter contacts 430, contacts 429, and 416. Shortly after the last impulse of the series, relay 404 restores and completes a circuit from ground on conductor 381, contacts 425 and 428 for rotary magnet 407. Magnet 407 energizes and steps the wipers in on the first set of contacts of the called level and at the same time opens the locking circuit of relay 405 at contacts 430.

In case the first trunk of the group is busy, the test wiper of the selector will encounter ground on the test contact and relay 405 will operate from this ground over contacts 414, 430, and 427. Relay 405 will again complete a locking circuit for itself and close a circuit for magnet 407 which will energize to advance the wipers another step. The stepping operation will be repeated as often as the test Y wiper encounters a grounded contact. When an idle trunk is encountered, for example, the trunk comprising conductors 384-386, the tt wiper will find no ground and relay 401, no longer being shunted by ground on the test wiper, will operate in series with relay 405. The resistance of relay 401 is relatively high and relay 405 does not operate at this time. Relay 401 disconnects line relay 402 from conductors 380 and 383 at contacts 411 and 418, respectively, and extends these conductors by way of contacts 412 and 417 to the upper and lower wipers of the selector. Relay 401 also connects the test wiper to grounded conductor 381 at contads 415 for marking the seized trunk busy to other switches and for operating the cut-0R relay of the toll line. A point in the release circuit is opened at contacts 416 so that, on the restoration of relays 402 and 403, the release magnet cannot operate to restore the wiper to normal position. that the trunk selected is the one terminating in the toll line comprising conductors 391-392' of Fig. 3A, ground on the test wiper by way of conductor 384, and contacts 3 31 and 324' will operate relay 303 of the toll 'line. This relay will open the bridge including relay 302 which is normally connected across the trunk line, and thus prevent the operation of the associated lineswitch when current is sent over the toll line.

Referring now to the register-sender and position apparatus, it isto be noted that the register is so arranged that ground is disconnected from conductor 322 when the registered digit or 'have been tranmitted. Relay 13, consequently, releases, opens the sender starting circuit at contacts 22, and opens the holding circuit of relays 11 and 12 at contacts 23. Relay 11 restores and disconnects ground from conductors 29 and 30. Relay 12 restores and opens the circuit of relay 14 which also restores. Relay 208, after a short delay, releases responsive to the removal of ground from conductor 29. This relay opens the short circuit around relay 207 and opens a point in the circuit of relays 205 and 206. Relay 207 is thus momentarily bridged across the talking conductors of the trunk, but does not operate due to the high resistances in series with relay 301 which is normally bridged across thetrunlr. Relays 205 and`206 restore due to the removal of ground from conductor 30 and the opening of contacts 254. Relay 205 is provided with a copper slug on its core which makes the relay very slow to release. Relay 206 is provided `with a noninductive win which 1,ass,5ss

slightly slows up the release of the relay which, however, will release ahead of relays 205 and 209. The purpose of the slow release feature of relay 206 will be explained in more' detail inlater paragraphs as it has no utility iii t/he present connection. During the interval after relay 206 restores and before relays 205 and 209 restore, a circuit is closed from battery', resist-ance 211, contacts 256, 247, and 238, conductor 222, contacts 359 and 374, conductor 380, contacts 412, upper wiper of selector S, conductor 336, upper Winding of relay 301 (Fig. 3A) to ground. Relay 301 will operate momentarily and apply ringing current to the toll line at oo ntacts 309 and 312. Relays 205 and 209 will restore after a short interval as will relay 301 and the calling and toll line will be connected through the position apparatus. 'lhe ringing current a plied to the called toll line will operate the llne signal at the distant toll board and an operator at that point will answer the call. The inward operator may now talk with either the calling or called operator alone by operating one or the other of keys K1 or K2. The operation of key K1 to the left completes a circuit for relay 204 at contacts 241. Relay 204 disconnects the callingr toll line from the operators telephone set by opening contacts 235 and 236. The operation of key K2 to the left completes a circuit for relay 205 at contacts 243 and this relay opcrates to disconnect the called toll line from the operators telephone set by opening contacts 237 and 240.

On satisfying herself that the. calling and called operators are properly connected, the inward operator will withdraw from the connection by restoring key K3 to normal. Upon the restoration of key K3, the circuits for relay 351 and 352 will be opened since relay 209 at the position equipment has also rcstored. and these relays will deencrgize followed by the release of relay 203. Relay 354 and relay 355, however, will remain energized over their previously-traced locking circuits and will maintain the connection through the selector as described. The calling toll line will now be extended ythrough the link circuit and selector to the called toll line which l incidentallyY will be in normal condition with onz'toring After setting up a connection as above described, the inward operator may listen in at any time without interfering with the progress of the call. Key K3 is operated to the right, that is, to monitoring position and a circuit is completed by way of contact 395, conductor 219, and contacts 233 for relay 202. Relay 202 connects the receiver across the secondary Winding of induction coil IC at contacts 225 and 227. The primary winding of the coil is normally bridged across conductors 217 and 218 in series with a condenser, and since key K3-is operated, the conductors are connected to the upper and lower talking conductors of the link via contacts 393 and 394, respectively. The inward operator cannot talk over the connection, however, since the transmitter of her telephone set is not' connected up.

The monitoring key may also be employed for answering calls when the sender is associated with one of the link circuits. Under these conditions, it will be recalled that. relays 204 or 205 and relays 206, 208 and 209, or relays 206, 207, and 209 of the position appa ratus will be operated together with relays 351 and 352 of the link circuit. The answering key K3 of the link is then restored to normal and the relays are maintained over the auxiliary holding circuit previously traced. If the monitoring key of another link circuit is now operated, the talking conductors of the link will now be extended to the position circuit to which the operators telephone set is connected. Relays 351 and 352 of the second link will not be operated and the linelamp of the link will continue to glow. The inward operator may talk with the calling operator, however, since, as stated above, the operators telephone set (including transmitter) is connected to the position apparatus by relay 203 which is held up over the auxiliary circuit of the first link. When the sender completes its operation, the auxiliary circuit will be opened in the usual manner, thus connecting the first toll line through to the called line. The operators set will be disconnected by\the release of relay 203, although of course it will still be in monitoring connection with the second toll line. The operator will then operate the talking key of the second link and complete the connection as in the previous instance.

Recall the link from the operators set and connects it through to the contacts of the ringing key. A circuit may now be traced from battery, resistance 211, contacts 263 and 261, conductor 223, contacts 357, conductor 340, wiper 334, contacts 316, and upper winding of relay 301 to ground. Relay 301 will operate over 

